Bertil Åkesson (1928 – 2013)

Aquatic Oligochaetes, 1999

The origin and the position of the Clitellata in the phylogenetic system are the object of vigorous scientific debate. Since most extant Clitellata are either terrestrial or limnetic, the question arises which characters are specific adaptations to these environments and which are plesiomorphies taken from the annelid stem species. A promising approach is to study whether clitellate characters are present in terrestrial polychaetes as well. In fact, the terrestrial polychaetes Hrabeiella periglandulata Pizl & Chalupský, 1984 and Parergodrilus heideri Reisinger, 1925 have many features in common with the Clitellata, as does Stygocapitella subterranea Knöllner, 1934, which inhabits sandy beaches at the transition between the marine and terrestrial realms. These features include a prostomium lacking appendages, chaetae that are simple and short, an absence of parapodia, an epidermis without kinocilia, sensory cells with cilia that project only slightly beyond the cuticle or not at all, direct development, direct sperm transfer and eggs laid in cocoons. The nuchal organs so characteristic of polychaetes are either displaced into the body and reduced (S. subterranea, H. periglandulata) or absent (P. heideri). In H. periglandulata, the nervous system and the foregut also closely resemble those of the oligochaetes. These polychaetes are certainly not closely related and clearly do not belong to the Clitellata, as shown by their lack of a clitellum, the different structure and position of the reproductive organs and ultrastructural differences in the sperm. Hence their similarities to clitellates have most probably arisen by convergence. A hypothesis is presented explaining the evolution of the terrestrial polychaetes as a model for that of the Clitellata, documenting a primary terrestrial origin of the latter.

Estuarine, Coastal and Shelf Science, 1995

Animals greater than 1 mm, found among tangled tubes of Phyllochaetopterus socialis (Chaetopteridae) from Araçá Beach, São Sebastião district, Brazil, were studied for 1 year, with four samples in each of four seasons. They comprised 10 338 individuals in 1722•7 g dry weight of polychaete tubes, with Echinodermata, Polychaeta (not identified to species) and Crustacea as the dominant taxa. The Shannon-Wiener diversity index did not vary seasonally, only two species (a holothurian and a pycnogonid) showing seasonal variation. Ophiactis savignyi was the dominant species, providing 45•5% of individuals. Three other ophiuroids, the holothurian Synaptula hidriformis, the crustaceans Leptochelia savignyi, Megalobrachium soriatum and Synalpheus fritzmuelleri, the sipunculan Themiste alutacea and the bivalve Hiatella arctica were all abundant, but most of the 68 species recorded occurred sparsely. The assemblage associated with P. socialis was similar to the endofauna of the sponge Zygomycale parishii and the bryozoan Schizoporella unicornis, and to the epifauna of seaweed Sargassum cymosum, all of which occurred nearby. 1995 Academic Press Limited

2011

Brewer et al. (2011) recently demonstrated that the generic name Euzonus was being used in both Arthropoda (Diplopoda) and Polychaeta (Opheliidae) systematics and that the arthropod name was the senior synonym. The diplopod name Euzonus Menge, 1854, based on a single species, E. collulum Menge, 1854 from Baltic amber predates Euzonus Grube, 1866, established for E. arcticus Grube, 1866 from the Arctic Ocean. The Nomenclator Zoologicus (2005) verifies that both names are listed as uncorrected homonyms. Brewer et al. (2011) suggested that for time being, the genus Pectinophelia Hartman, 1938 could be used for those species of Polychaeta currently referred to the genus Euzonus. However, prior to Hartman's (1956) referral of these opheliids to the genus Euzonus, some species had been included in the genus Thoracophelia Ehlers, 1897 and this is clearly the next available name for polychaetes currently referred to Euzonus Grube. In the following paragraphs I summarize some key decision points in the taxonomic history of these opheliids, their referral to Thoracophelia, and why subgenera, as currently applied, are not necessary. The polychaetes that have been referred to Euzonus are unusual among the Opheliidae in having the body divided into three distinct regions: (1) an anterior cephalic region formed of the prostomium and first two setigers; (2) a swollen thoracic region, usually through setigers 2-10; and (3) a long narrow posterior region with a distinct ventral groove; sometimes the posterior pygidial region is enlarged or modified. Branchiae are limited to the posterior region, but are typically absent from the posteriormost segments. Santos et al. (2004) also noted that all species of these opheliids have a lateral modification of setiger 10, either as a flap arising from the body wall or with rows or patches of papillae. Two species referred to the genus Lobochesis Hutchings & Murray, 1984 also share these characters and were referred to Euzonus by Santos et al. (2004). This synonymy was further supported as part of a cladistic analysis of opheliids by Sene Silva (2007) who demonstrated that the two species of Lobochesis were nested within a monophyletic clade of Euzonus species. The current arrangement of species and subgenera of the opheliids referred to

Journal of Natural History, 2005

Marine Ecology, 2005

Physiological Genomics, 2016

Armleuchteralgen, 2015

This chapter presents a review of the most significant steps in charophyte evolution and its fossil record, which is amongst the most complete in fossil algae. It provides enough data to document the history of the group from the Silurian until the present. Fossil charophyte remains include mainly their calcified fructifications, i.e. utricles and gyrogonites, but also their fossil thalli. Palaeozoic represents the time when charophytes reached a maximum of diversity in the Bauplan of their fructifications, with the coexistence of three charophyte orders, Sycidiales, Moellerinales and Charales. The extinction of two of these orders at the end of the Palaeozoic led to a single type of fructification, the porocharacean gyrogonite that represents the charalean ancestor of all post-Palaeozoic charophytes. However, this ancestor diverged soon in two evolutionary lines, Polyplacata and Monoplacata, based on the presence of a multicellular vs single basal plate of the gyrogonite. This fundamental difference can be assumed representing two alternative types of female gametogenesis. Charophytes with a composite basal plate, the Polyplacata, developed diverse morphologies at the base of the Mesozoic (Triassic-Jurassic), most of them are traditionally ranged within the porocharaceans, characterised by an apical opening. These polyplacate porocharaceans are considered the ancestors of extant Nitella and Tolypella (sensu stricto), recorded already in the Jurassic and Cretaceous respectively. Monoplacata diversified in several steps, the first in the Upper Jurassic and Lower Cretaceous with the appearance of the utricle-bearing clavatoraceans, and the appearance of the first characean genera with a single basal-plate, including the oldest known Sphaerochara (equivalent to Tolypella sect. Rothia). The Clavatoraceae family dominated the wetlands on the Tethyan islands during the Lower Cretaceous relegating the porocharaceans to brackish environments. At the beginning of the Late Cretaceous (Cenomanian and Turonian) there is a gap in the fossil record. After this gap the monoplacate Characeae underwent an important radiation and expanded with the appearance of many genera including modern Chara, Lamprothamnium, and Lychnothamnus. This radiation occurred in parallel with the extinction of a few last species that remained from clavatoraceans and porocharaceans near the Cretaceous-Tertiary boundary. Genus Nitellopsis is documented since the lowermost Tertiary. Characeans reached their maximum of diversification in the Middle Eocene, with numerous genera whose gyrogonites were quite different from the modern ones. These morphological types regressed during the Late Eocene and the Early Oligocene when a global climatic shift occurred. Afterwards the charophytes were progressively reduced to the morphologies of the seven modern genera. Hence the Neogene to recent flora appears as an impoverished remnant of the flourishing of charophytes in the geological past.

Hydrobiologia, 2005

Annelid phylogeny is one of the larg est unresolved problem s within the Metazoa. This is du e to the enorm ous age of this taxon and also strongly influenced by the cu rrent discu ssion on the position of the Arthrop oda, which traditionally is hypothesized to be the annelid sister taxon. Within the fram ework of recent discussions on the position of the Annelida, the grou nd pattern of this taxon is either a clitellate-like, parapodia-I ess dwelling organism or an organisms that resembles errant polychaetes in having parapodia and gills and probably being a predator. To solve this problem different attem pts have been made in the pa st, cladistic analysis, scenario based plausibility considerations and a successive search for sister taxa base on isol ated characters. These attem pts are presented and critically discussed. There is at least strong sup port for the Annelida as wells as for several of its taxa above the level of traditional families; the monophyly of the Polychaeta, however, remains questionable.

2001

The paper summarises information on the life history of tubeworms (Serpulidae and Spirorbidae). Topics reviewed are sexuality patterns, asexual reproduction, gamete attributes, fecundity, spawning and fertilisation, larval development and morphology, larval ecology and behaviour (including larval swimming, feeding, photoresponse, and defences), brooding, settlement and metamorphosis, longevity and mortality. Gonochorism, simultaneous and sequential hermaphroditism are found in the group, the last pattern being apparently under-reported. Asexual reproduction commonly leads to the formation of colonies. The egg size range is 40-200 11m in serpulids and 80-230 11m in spirorbids. The sperms with spherical and with elongated heads correspond, respectively, to broadcasting and brooding. Variability of brooding methods in serpulids has been grossly under-reported and even exceeds that of spirorbids. Development is similar in feeding and non-feeding larvae and the developmental events are easily reproducible in the laboratory until the onset of competency, after which larvae require specific cues to proceed with settlement and metamorphosis. Settlement is affected by both non-specific and substratum-specific cues (conspecifics, microbial film, other organisms). Initial rapid juvenile growth slows down at later life stages. The growth rates are affected both by factors acting after the settlement and those experienced during the larval stage. Maturation is reached at a certain body size and depends on the factors controlling growth. Longevity varies from several months in small serpulids and spirorbids to 35 yr in the largest serpulids. Mortality is highest during the early embryonic and juvenile stages. The egg-size distribution in serpulimorph polychaetes is bimodal but the modes do not correspond to feeding and non-feeding development and egg sizes of species with feeding and non-feeding larvae partially overlap. This pattern may be explained by high interspecific variability in the organic content of eggs and/or facultative larval feeding of some serpulids. Planktonic development is strongly correlated with larval feeding, and planktonic lecitotrophy is rare. The potential selective advantage of larval feeding is in the flexibility of the duration of the competent stage that increases the possibility to locate suitable substrata. As in other groups, small body size correlates with simultaneous hermaphroditism, brooding, E. K. KUPRIY ANOVA, E. NISHI, H. A. TEN HOVE & A. V. RZHAVSK Y and non-feeding development. Broader generalisations require better knowledge of the life history of a greater number of species. Integration of phylogenetic analyses into life-history studies should help to clarify the direction of life-history transitions in this group and determine whether phylogenetic constraints can account for the observed life-history patterns.

Reproductive Strategies and Developmental Patterns in Annelids, 1999

The reproduction and larval development of spioniform polychaetes are reviewed. Asexual reproduction is relatively rare, being reported for only eight species belonging to the genus Pygospio and some polydorids. Both architomy and paratomy are known, with the latter limited to small species of Pseudopolydora (sometimes referred to Polydorella) and one species of Polydora. Architomy is often the primary form of reproduction in Pygospio elegans and contributes to the maintenance of large populations. Three types of eggs (thin egg envelopes, thick egg envelopes, smooth or reticulated, and thick egg envelopes, honeycombed), two types of oogenesis (extraovarian and intraovarian), and two types of sperm (ect-aquasperm and introsperm) occur in spioniforms. Egg and sperm type are restricted to specific clades. Eggs with thickened egg envelopes appear to be limited to spioniforms, whereas the thin egg envelope found in some spionids occurs in other polychaete families, suggesting that thin egg envelopes are plesiomorphic for spionids. Spermatophores occur in the spionid subfamily Spioninae and are formed in the male nephridia. Spioniforms exhibit a diversity of reproductive and larval patterns including broadcast spawning, external egg masses, brooding in capsules in tubes of females and brooding on the bodies of females. Poecilogony is unusually common in the Spionidae. A phylogenetic analysis demonstrates that reproductive and larval characters, when used in combination with selected adult characters, provide a more complete database to evaluate systematic and phylogenetic relationships than only adult morphology. Preliminary results of parsimony suggest that the Spionidae are paraphyletic and that its definition and the status of related spioniform polychaetes needs to be reassessed with regard to family level classification. Sexual Locality References zone reproduction Pygospio elegans Architomy Variable N/A Yes Northern Rasmussen